Referring initially to FIG. 1, bucket assemblies 100 have been traditionally used with rigging assemblies 102 that use a lower spreader bar 104 positioned above the rear attachment points 106 (usually trunnion type connections with trunnion links are provided) of the bucket assembly 100 to help keep the hoist chains 108, from which the bucket assembly 100 is suspended, from contacting the edges 110 of the walls such as the sidewalls 112 of the bucket assembly 100 during use such as when material is loaded into or dumped out of the bucket 114. If such contact or rubbing occurs as the pulling chains 116 (shown to be attached via a clevis link) make the bucket move, the chains 108 may wear over time and need replacement, requiring downtime for maintenance that could lead to loss profits for a mining operation or the like. Also, the spreader bar 104 helps to position the chains 108 so that the chains do not inhibit the filling of the bucket 114 or dumping of the bucket 114.
However, such spreader bars 104 are very heavy, putting a load on the hoist chains 108 and on the machine (not shown) using the bucket assembly 100, and may themselves wear. This too can lead to required maintenance. Also, the machine may have to exert more energy, resulting in higher operation costs for the mining operation or the like. Furthermore, the weight of the spreader bar 104 limits the capacity of the bucket 114, affecting the efficiency of the mining operation.
Consequently, various designs have been developed to eliminate the need for a lower spreader bar 104. One such design has included altering the geometry of the rear of the bucket 114, such as by angling, beveling or mitering the sidewall 112 as desired near the rear of the bucket 114, to decrease the risk of the chain 108 at a rear attachment point 106 of the bucket 114 from rubbing on an edge 110 of the bucket 114. However, these buckets 114 tend to be long, rendering them less efficient than desirable when loading the bucket 114 with material in use (e.g. it may take longer to fill or empty such buckets). Also, the placement of the attachment points 106 do not maintain balance of the bucket 114 as material is loaded into the bucket in a desirable manner. Another design has placed the attachment points 106 or trunnions inside of the bucket 114, but this tends to limit or interfere with the loading or dumping of material into or out of the bucket 114. In other cases, the trunnions are placed on the rear wall but this may not be ideal in terms of maintaining balance of the bucket as material is loaded into the bucket.
Accordingly, it is desirable to develop a better design for a dragline bucket to help eliminate the need for a spreader bar in the rigging assembly than has yet been devised.